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Re: shim6 @ NANOG (forwarded note from John Payne)
On 1-Mar-2006, at 11:55, David Barak wrote:
What's broken today is that there's no mechanism available for people who don't qualify for v6 PI space to multi-home. That's what shim6 is trying to fix.--- Joe Abley <email@example.com> wrote:I'm just one guy, one ASN, and one content/hostingnetwork. But Ican tell you that to switch to using shim6 insteadof BGP speakingwould be a complete overhaul of how we do things.You are not alone in fearing change.It isn't fearing change to ask the question "it's not broken today, why should I fix it?"
That's an example of a simple topology where the routing system might be expected to reconverge rapidly.It seems reasonable to say that in some cases shim6 re-homing transitions will be faster than the equivalent routing transition in v4; in other cases it will be shorter. Depends on the network, and how enthusiastically you flap, perhaps.A - X - Y - B \ | \ | / W - Z A and B are hosts, W-Z are ISPs On what basis would you say that in the event of a network outage in Y, communication between A and B will be faster than the routing transition?
However, it's not hard to find examples in today's v4 Internet where reconvergence following a re-homing event can take 30 to 60 seconds to occur. In the case where such an event includes some interface flapping, it's not that uncommon to see paths suppressed due to dampening for 20-30 minutes.
I would expect (in some future, hypothetical implementation of shim6) that the default failure detection timers to start rotating through the locator set far sooner than 30-60 seconds.
We have peering arrangements with about 120 ASNs. How do we mix BGP IPv6 peering and Shim6 for transit?You advertise all your PA netblocks to all your peers.And maintain 120 different context tables on each host?
No; maintain one address per PA netblock on each host.
There's a vast difference in impact on the state held in the core between deaggregating towards direct peers, and deaggregating towards transit providers and having the deaggregated swamp propagated globally.You avoid it completely, and use PA space in every POP. You can still announce PA space from other POPs to peers, if you want to retain your tunnels.Wait a second - doesn't that deaggregation bring back the "lots of small routes" business which the whole v6 hierarchical addressing model was supposed to fix? If we're in the world of deaggregates anyway, why not just ditch the addressing model instead of accepting its limitations in this way?